Warfarin Drug-Drug Interactions with Amiodarone and Tramadol in a Patient with Paroxysmal Atrial Fibrillation: A Case Report

Amiodarone and tramadol are known to have drug-drug interactions that potentiate the effects of anticoagulant warfarin. Herein we report a case which suggests increasing prothrombin time-international normalized ratio (PT-INR) PT-INR/dose due concomitant administration warfarin, amiodarone (a cytochrome P450 2C9 inhibitor) (an enhancer warfarin). A 72-year-old woman underwent emergency surgery following suspected non-obstructive mesenteric ischemia, diagnosis was confirmed. After surgery, patient given 2 mg/day WF, tramadol/acetaminophen, followed by amiodarone. dose triple combination, PT-INR increased over 7.02 (above upper limit laboratory). The physician consulted pharmacist for adjustment, recommended reduction in 0.5 mg. restarting controlled 1.66–2.02. However, from 1.22 3.32–4.04 compared initial dose. results suggest these enhanced may be inhibition WF metabolism. Although resection small intestine, oral vitamin K1 were observed one day after administration. In conclusion, frequent monitoring, intervention such as assessment adjustment this should beneficial during anticoagulation therapy when multiple medications with present.